The field of the invention relates to a method and apparatus for characterizing comparators and more specifically to a method and apparatus for characterizing an active track and latch sense-amp, comparator, in a one-time programmable (OTP) salicided poly fuse array.
An OTP (one time programmable) ROM is an array of memory cells having fuse or anti-fuse fusible links wherein fuse links are opened by blowing the fuse by applying a writing current. Once a fuse link is blown the impedance of the link is much higher than that of an unblown fuse. Track and latch sense amplifiers or comparators are coupled to the outputs of the OTP fuses. These comparators are used to compare two voltages within the poly fuse array. Testing of these comparators is important in that characterization of the properties of the comparator and prior art methods of characterizing a sense-amp require a dedicated test chip designed solely or partially for the purpose of testing sense-amp, which unfortunately adds complexity to the circuit.
These comparators are designed to compare two voltages. The voltages are in the order of a few millivolts above ground level and as a result can be affected by noise during a read procedure. Therefore, a test chip used for testing a sense-amp sometimes produces inadequate results because of the errors caused by the noise.
A method of testing the track and latch comparators within the circuit would be to build a stand alone comparator with its test circuit in order to characterize its performance, unfortunately this would take the comparator out of its context of utilization resulting in an improperly characterized device and potentially incorrect results.
The comparator requires a set of pulses that are generated by a state machine in order to operate successfully. All reference inputs (inxe2x88x92) to the comparator are tied to single node while all the positive inputs (in+) are independent from each other. This makes characterization of the track and latch comparator difficult in that each of the input to the track and latch comparator are electrically unbalanced. As a result unbalanced testing of the comparator within the circuit is required for proper device understanding.
It would therefore be advantageous to be able to characterize an active sense-amp comparator within a memory itself without affecting the performance of the sense-amp comparator.
In accordance with the invention there is provided an integrated circuit comprising:
a comparator including: a comparison circuit, a first input port, a second input port, and an output port; and,
a switch integral to the integrated circuit and in electrical communication with the first input port for switchably selecting between a plurality of input signals wherein one input signal is in accordance with the circuit operation requirements and another input signal is solely for use in testing of the comparator.
In accordance with another aspect of the invention there is provided a non-intrusive method of characterizing a comparator within an integrated circuit comprising the steps of:
providing power to the comparator;
providing switches within the integrated circuit for controlling various test input signals to the comparator;
switching a first control signal to the first input port of the comparator and monitoring an output signal provided at the output port;
switching a second control signal to the second input of the comparator and monitoring an output signal provided at the output port.